To determine the risks of general anesthesia and elective surgical procedures in patients with histories of hypertension, 676 consecutive operations in a series of patients more than 40 yr old were studied. All patients were examined preoperatively, monitored intraoperatively and closely followed postoperatively. Patients with higher preoperative blood pressure values had larger absolute intraoperative blood pressure decreases but the mean intraoperative systolic pressure nadirs in patients with tightly-controlled hypertension (100 .+-. 2 torr) did not differ from those in patients with persistent treated (97 .+-. 3 torr) or untreated (98 .+-. 2 torr) mild to moderate hypertension. Among the 3 groups of patients, the needs for intraoperative adrenergic agents or fluid challenges (20, 33 and 27%, respectively) and the incidence of perioperative hypertensive events (27, 25 and 20%, respectively) were not significantly different. Multivariate analysis of data for the patients with histories of hypertension showed that neither the preoperative in-hospital diastolic nor preoperative in-hospital systolic blood pressure valves independently correlated with any of these 3 indices of perioperative blood pressure lability, with the development of cardiac arrhythmias, ischemia or failure, or with postoperative renal failure. Effective intraoperative management may be more important than preoperative hypertensive control in decreasing clinically significant blood pressure lability and cardiovascular complications in patients who have mild to moderate hypertension.